JP2006105641A - Backup power supply system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a backup power supply system that can determine the deterioration state of a lithium secondary battery constituting a backup power supply, without using resistors or power supplies for energizing a large current. <P>SOLUTION: A CPU in a microcomputer 13 supplies backup power from a backup power supply 3 to a load 5 via a diode 6 for a fixed amount of time by turning on the switch 6, even if a load voltage determined by subtracting the voltage drop of a diode 4 from the voltage of a main power supply 1 is higher than a preset voltage, when it is judged that the voltage of the main power supply 1 is lower than that of the backup power supply 3. The CPU calculates the internal resistance of each cell from current detected, while supplying backup power and a cell voltage for composing the backup power supply 3, corrects the temperature by temperature detected by a thermistor 14, and decides the deterioration state of each cell from the correspondence relation between the internal resistance and deterioration state, after a predetermined temperature correction. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backup power supply system, and more particularly, a backup power supply system having a plurality of lithium secondary batteries and having a backup power supply that is charged in a fixed state by a main power supply that supplies power to a load via a diode About.

  In a lithium secondary battery used for backup applications such as an electronically controlled brake (ECB) system, a function for determining whether or not the lithium secondary battery has deteriorated is indispensable in order to ensure vehicle safety. In this type of backup application, a relatively short-time power supply function is required from a backup power source composed of a lithium secondary battery. It is conceivable to determine this.

  On the other hand, since the internal impedance of a lithium secondary battery is small, it is difficult to measure the internal resistance with a very small current. Conventionally, a lithium secondary battery is discharged or charged / discharged with a certain amount of large current, and lithium A method of calculating the internal resistance of the secondary battery has been used (see, for example, Patent Documents 1 and 2).

JP 2000-270408 A Japanese Patent Laid-Open No. 2000-019233

  However, the conventional method requires a resistor and a power source that conduct a large current to determine the deterioration state of the lithium secondary battery that constitutes the backup power source. Therefore, there is a problem that the space is increased in size.

  An object of the present invention is to provide a backup power supply system capable of determining a deterioration state of a lithium secondary battery constituting a backup power supply without using a resistor or a power supply for energizing a large current in view of the above case. .

  In order to solve the above problems, the present invention includes a backup power source that has a plurality of lithium secondary batteries and is charged in a constant charge state by a main power source that supplies power to a load via a first diode; Load voltage detection means for detecting a load voltage applied to the load from the main power supply via the first diode, a switch and a second diode, and power from the backup power supply to the load First switching means for supplying, current detection means for detecting current flowing in the backup power supply, voltage detection means for detecting the voltage of a lithium secondary battery constituting the backup power supply, and temperature of the backup power supply Temperature detecting means for detecting the load voltage, and when the load voltage detected by the load voltage detecting means is determined to be lower than a preset voltage, Control means for controlling the switch of the first switching means to be in an ON state so as to supply backup power from the power supply to the load through the second diode of the first switching means for a certain period of time. And the control means turns on the switch of the first switching means even when the load voltage is higher than the set voltage when the voltage of the main power supply is determined to be lower than the voltage of the backup power supply. The backup power from the backup power source is supplied to the load through the second diode for a certain period of time, and the current detected by the current detection means and the cell voltage detection means during the backup power supply are detected by the cell voltage detection means. The internal resistance of the lithium secondary battery is calculated from the voltage, and the temperature is corrected based on the temperature detected by the temperature detecting means. Characterized in that the relationship of the internal resistance after degrees corrected and deterioration state determining the deterioration state of the lithium secondary battery.

  In the present invention, when it is determined by the control means that the load voltage detected by the load voltage detection means is lower than a preset voltage, and even when the load voltage is higher than the preset voltage, the voltage of the main power supply When it is determined that the voltage is lower than the voltage of the backup power supply, the switch of the first switching means is controlled to be turned on so that the backup power from the backup power supply is loaded via the second diode of the first switching means. Is supplied for a certain period of time, and functions as a backup power supply system for the load. At this time, a load voltage defined as a voltage applied to the load from the main power supply via the first diode is regarded as a voltage of the main power supply, and a second voltage is detected from the voltage of the lithium secondary battery detected by the voltage detection means. The voltage obtained by subtracting the voltage drop of the diode can be regarded as the backup power supply voltage. Further, the control means calculates the internal resistance of the lithium secondary battery constituting the backup power source from the current detected by the current detection means during the supply of backup power and the voltage detected by the cell voltage detection means. The internal resistance is corrected by the temperature detected by the temperature detecting means. Then, the deterioration state of the lithium secondary battery is determined from the correspondence relationship between the predetermined internal resistance after temperature correction and the deterioration state.

  In the present invention, the control means may determine the deterioration state of the lithium ion battery every fixed time for supplying the backup power from the backup power source to the load. A reference voltage source for generating a reference voltage lower than a voltage supplied to the load from the backup power supply, and a second switching unit for switching the load voltage detected by the load voltage detecting unit to the reference voltage generated by the reference voltage source; The control means includes a first switching means so that the load voltage detecting means detects the reference voltage of the reference voltage source when the switch of the first switching means is turned on and the backup power from the backup power supply is supplied to the load. The two switching means may be switched to determine whether the load voltage detecting means and the first switching means are operating normally.

  According to the present invention, the internal resistance of the lithium secondary battery constituting the backup power source is calculated by the control means from the current detected by the current detection means during backup power supply and the voltage detected by the cell voltage detection means. Since the calculated internal resistance is temperature-corrected by the temperature detected by the temperature detecting means, the deterioration state of the lithium secondary battery is determined from the correspondence between the predetermined internal resistance after the temperature correction and the deterioration state. In addition, it is possible to obtain an effect that the deterioration state of the lithium secondary battery constituting the backup power source can be determined without using a resistor or a power source for energizing a large current.

  Embodiments in which the present invention is applied to a backup power supply system for an electronically controlled brake system of an automobile will be described below with reference to the drawings.

(Constitution)
As shown in FIG. 1, electric power is always supplied to the electronically controlled brake system serving as the load 5 from a main power source 1 such as a lead storage battery via a diode 4. The backup power supply system 20 of the present embodiment controls the backup power supply 3 in which a plurality of lithium ion batteries are connected in series, and the supply of backup power from the backup power supply 3 to the load 5. And a microcomputer 13 for determining a deterioration state of a lithium ion battery (hereinafter referred to as a cell).

  The terminals of the cells constituting the backup power supply 3 are connected to the input side of the cell voltage detection circuit 12. The cell voltage detection circuit 12 selects a differential amplifier circuit that converts the voltage of each cell into a voltage based on the ground (GND) of the backup power supply 3, and selects the voltage of each cell converted to the ground reference to the microcomputer 13. And a multiplexer for outputting to the receiver. Therefore, the microcomputer 13 can take in the voltage of each cell as a digital value via the A / D converter.

  The thermistor 14 is fixed to one cell arranged in the center among the cells constituting the backup power supply 3. Further, one end of a current detection circuit 11 such as a Hall element that detects a current flowing through the backup power supply 3 is connected to the positive terminal of the backup power supply 3. For this reason, the microcomputer 13 can take in the temperature of the cell of the backup power source 3 and the current flowing through the backup power source 3 (each cell) as digital values via the A / D converter.

  The other end of the current detection circuit 11 is connected to a backup switching circuit 15 for supplying backup power from the backup power supply 3 to the load 5 and a charge control circuit 2 for controlling charging from the main power supply 1 to the backup power supply 3. Has been. The backup switching circuit 15 has a switch 6 and a diode 7 each composed of an FET and a resistor. When the high level signal is output from the microcomputer 13 to the gate of the FET, the switch 6 is turned on, and the backup power from the backup power source 3 is supplied to the load 5 via the diode 7. On the other hand, the charge control circuit 2 is also configured to include a switch (not shown) constituted by an FET and a resistor and a diode (not shown) having a reverse direction to the diode 7. The charge control circuit 2 and the microcomputer 13 are connected by a signal line (not shown), the switch of the charge control circuit 2 is turned on by the output of the high level signal from the microcomputer 13, and the backup power supply 3 is connected to the main power supply 1. It is charged with the electric power.

  Further, the backup power supply system 20 includes a load voltage detection circuit 8 that detects a load voltage applied to the load 5 (voltage at point A in FIG. 1), and a constant voltage reference voltage lower than the voltage of the backup power supply 3. A reference voltage source 9 generated from the backup power source 3, and a changeover switch circuit 10 having a switch composed of an FET and a resistor and switching the load voltage detection circuit 8 to output either the load voltage or the reference voltage. ing. The load voltage detection circuit 8 receives the output voltage of the changeover switch circuit 10 and the source side (output side) voltage of the switch 6 of the backup changeover circuit 15 (voltage at point B in FIG. 1). Is output to the microcomputer 13.

  The microcomputer 13 is a CPU that functions as a central processing unit, a basic control program for the backup power supply system 20 and a ROM that stores program data such as setting voltage and map information described later, a RAM that functions as a work area for the CPU, and a plurality of An A / D converter and a D / A converter are included. As described above, the microcomputer 13 is connected to the current detection circuit 11, the cell voltage detection circuit 12, and the thermistor 14, and is also connected to the main power supply 1 for taking in the voltage of the main power supply 1. The detected data can be taken in via the A / D converter. The microcomputer 13 is connected to the charge control circuit 2, the backup switching circuit 15, and the changeover switch circuit 10 by signal lines, and can control these operations by outputting a high level signal or a low level signal. . Furthermore, the microcomputer 6 is connected to the vehicle-side microcomputer via an interface (not shown).

(Operation)
Next, with reference to a flowchart, the operation of the backup power supply system 20 will be described focusing on the CPU of the microcomputer 13 (hereinafter simply referred to as CPU). When the operating power is turned on to the microcomputer 13, the CPU executes a backup routine shown in FIG. During normal operation (when backup power is not supplied from the backup power supply 3 to the load 5), the signal line between the microcomputer 13 and the changeover switch circuit 10 and the connection between the microcomputer 13 and the backup changeover circuit 15 are also shown. The signal line is in a low level state (a state in which the CPU does not output a high level signal).

  As shown in FIG. 2, in the backup routine, first, the voltage of the main power supply 1 is captured in step 102, and the voltage of each cell is captured via the cell voltage detection circuit 12 in step 104. Next, at step 106, it is determined whether or not the voltage of the main power source 1 captured at step 102 is equal to or higher than the sum of the voltages of each cell captured at step 104, that is, the voltage of the backup power source 3.

  If the determination in step 106 is affirmative, the load voltage is fetched from the load voltage detection circuit 8 in the next step 108. At this time, the signal line between the microcomputer 13 and the changeover switch circuit 10 is in a low level state, and the changeover switch circuit 10 is connected to the voltage at the point A in FIG. ) Is output. Since the signal line between the microcomputer 13 and the backup switching circuit 15 is also in the low level state and the switch 6 is in the open state (off state), the other input side of the load voltage detection circuit 8 is almost at the GND level. Is input. For this reason, the load voltage detection circuit 8 outputs the higher load voltage to the microcomputer 13.

  Next, in step 110, it is determined whether or not the load voltage captured in step 108 is equal to or higher than a preset voltage (stored in the ROM and developed in the RAM in the initial setting process). If the determination is affirmative, the power from the main power source 1 can cover the power consumption of the load 5 and it is not necessary to supply the backup power from the backup power source 3 to the load 5. A charge processing subroutine is executed to maintain a constant charge state.

  On the other hand, when the determinations in step 106 and step 110 are negative, a backup power supply processing subroutine for supplying backup power from the backup power source 3 to the load 5 for a certain period of time is executed in step 300.

  As shown in FIG. 3, in the charging processing subroutine, in step 202, the voltage of each cell is taken in via the cell voltage detection circuit 12, and in step 204, the state of charge (SOC) of each cell is calculated. Next, in step 206, in order to prevent the cells constituting the backup power supply 3 from falling into an overcharged state, it is determined whether or not all the cells are below a predetermined SOC (for example, 98%). If the determination is affirmative, a high level signal is output to the signal line connected to the charge control circuit 2, the charge processing subroutine is terminated, and the process returns to step 102. As a result, a switch (not shown) of the charge control circuit 2 is turned on, and the backup power source 3 is charged by the power from the main power source 1 and is maintained in a constant charge state during normal times.

  As shown in FIG. 4, in the backup power supply processing subroutine, in step 302, a high level signal is output to the signal line to the backup switching circuit 15, a low level signal is output to the signal line to the charge control circuit 2, A switch switching process for outputting a high level signal to the signal line to the selector switch circuit 10 is executed. As a result, the switch 6 is turned on, the backup power from the backup power supply 3 is supplied to the load 5, and the backup power supply 3 is in the discharge state. Therefore, the switch (not shown) of the charge control circuit 2 is turned off. Thus, the charging current from the main power source 1 to the backup power source 3 whose current direction is reversed is cut off. Further, the changeover switch circuit 10 switches the voltage at point A (load voltage) in FIG. 1 to the reference voltage of the reference voltage source 9 and outputs it to the load voltage detection circuit 8. The voltage of the backup power source 3 (the voltage at point B in FIG. 1) and the reference voltage are input to the load voltage detection circuit 8, and the voltage of the backup power source 3 having a voltage higher than the reference voltage is input to the microcomputer 13. In step 302, time measurement by an internal clock is started.

  Next, in step 304, the output from the load voltage detection circuit 8 is captured. In step 306, whether or not the captured voltage value (digital value) is greater than a preset reference voltage value (digital value of the reference voltage). Thus, it is determined whether the backup switching circuit 15 and the load voltage detection circuit 8 (and the changeover switch circuit 10) are operating normally.

  That is, by the switch switching process in step 302, the reference voltage is input to one input side of the load voltage detection circuit 8 via the changeover switch circuit 10, and the other input side is connected via the switch 6 in the on state. Since the voltage of the backup power supply 3 having a voltage higher than that of the reference power supply is input, the voltage output from the load voltage detection circuit 8 should be output higher than the reference voltage. Since the CPU knows the reference voltage value as the program data, if the voltage value acquired in step 304 is larger than the reference voltage value, the backup switching circuit 15 and the load voltage detection circuit 8 (and the changeover switch circuit 10) operate normally. If the voltage value acquired in step 304 is smaller than the reference voltage value, at least one of the backup switching circuit 15 and the load voltage detection circuit 8 (and the changeover switch circuit 10) operates abnormally. It can be determined that

  If the determination in step 306 is affirmative, the process proceeds to step 310; ) Is informed that there is an abnormality, and proceeds to step 310. When the vehicle-side microcomputer causes the display control unit of the installation panel to display an abnormality, the driver can know that there is an abnormality in the backup power supply system 20.

  In step 310, the voltage value of each cell constituting the backup power supply 3 is fetched from the cell voltage detection circuit 12, the temperature value of the cell is fetched from the thermistor 14, and the current value flowing from the current detection circuit 11 to the backup power supply 3 is fetched. Measurement processing is performed and stored in the RAM. Next, in step 312, the SOC of each cell is calculated from the voltage value of each captured cell using a map in which the correspondence between the voltage value and the SOC is determined in advance, and in step 314, the backup power source 3 is turned on. It is determined whether or not all the cells that are configured have a predetermined SOC (for example, 20% or more). If the determination is negative, the process proceeds to step 318 to prevent overdischarge. If the determination is affirmative, a predetermined time (for example, 10 minutes) set in advance after the time measurement is started in step 302 in step 316. It is determined whether or not elapses.

  If a negative determination is made in step 316, the backup power of the backup power supply 3 is continued to be supplied to the load 5 and the measurement of the backup power supply 3 is continued to return to step 310. If a positive determination is made, the process proceeds to step 318. . In step 318, a low level signal is output to the signal line to the backup switching circuit 15, a high level signal is output to the signal line to the charge control circuit 2, and a low level signal is output to the signal line to the changeover switch circuit 10. The switch switching process is executed. That is, by outputting a signal opposite to that in step 302, the switch 6 of the backup switching circuit 15 is turned off, the switch (not shown) of the charging control circuit 2 is turned on, and the input of the changeover switch circuit 10 is set as shown in FIG. Switch to the voltage at A. As a result, charging is started so that each cell of the backup power supply 3 whose charging state has been lowered becomes a constant charging state.

  Next, in step 320, the internal resistance value of each cell is calculated from a plurality of sets of time-lapse data composed of the voltage value and the current value measured in step 310 (stored in the RAM). Such calculation of the internal resistance value can be obtained by using, for example, Ohm's law and an approximate straight line by the method of least squares. In the next step 322, the internal resistance value calculated in step 320 is corrected to an internal resistance value at room temperature (25 ° C.), for example, based on the average value of the temperature values measured in step 310. Next, in step 322, the SOH of each cell is calculated from the internal resistance value calculated in step 322 using a map in which the correspondence relationship between the internal resistance value at normal temperature and the state of health (SOH) is determined in advance. Is calculated.

  Next, in step 326, it is determined whether each cell is equal to or greater than a predetermined SOH (for example, 40%). If the determination is affirmative, the backup power supply processing subroutine is terminated and the process returns to step 102. If the determination is negative, the vehicle-side microcomputer is informed in step 328 that the backup power supply (cell) of the backup power supply system 20 has deteriorated. The backup power supply processing subroutine is terminated and the process returns to step 102. As the vehicle-side microcomputer causes the display control unit of the installation panel to display the deterioration, the driver can know that the backup power supply of the backup power supply system 20 has deteriorated.

(Action etc.)
Next, the operation and the like of the backup power supply system 20 of the present embodiment will be described.

  In the backup power supply system 20 of the present embodiment, the cells constituting the backup power supply 3 are charged to a fixed charge state from the main power supply 1 via the charge control circuit 2 at normal times, and from the main power supply 1 via the diode 4. Electric power is supplied to the load 5. On the other hand, when the load voltage is smaller than the set voltage (step 110) and even when the load voltage is larger than the set voltage, the voltage of the main power source 1 is smaller than the voltage of the backup power source (step 106). Is supplied to the load 5 for a certain period of time (steps 300 and 316). When this backup power is supplied, the voltage of each cell constituting the backup power supply 3, the current flowing through the backup power supply 3, and the temperature of the backup power supply 3 are captured (step 310). Then, the internal resistance value of each cell is calculated (calculated) to correct the temperature of the internal resistance value, and the SOH of each cell is calculated using a map in which the correspondence between the internal resistance value and SOH is determined in advance. Since the SOH of the cell is determined (steps 320 to 326), it is possible to determine the deterioration state of each cell constituting the backup power source without using a resistor or a power source for supplying a large current as in the prior art.

  Further, in the backup power supply system 20 of the present embodiment, switch switching processing is performed to capture the output from the load voltage detection circuit 8, and normal operation determination of the backup switching circuit 15, load voltage detection circuit 8, and changeover switch circuit 10 is performed. (Steps 302 to 306), it is possible to detect a failure of the backup switching circuit 15, the load voltage detection circuit 8, and the changeover switch circuit 10 by the switch switching process. Further, since the backup power supply system 20 determines the deterioration state of each cell at every predetermined time when the backup power is supplied to the load 5, it is possible to monitor the deterioration state of each cell at any set time. It is. Further, since backup power is supplied to the load 5 when all the cells are equal to or higher than the predetermined SOC (step 314), an overdischarge state can be prevented.

  In the present embodiment, the configuration of taking in the voltage of the main power supply 1 has been illustrated for easy understanding of the present invention. However, since the voltage drop due to the diode 4 is known, the voltage of the main power supply 1 is determined in step 102. Alternatively, the voltage (load voltage) at point A in FIG. 1 obtained by subtracting the voltage drop of the diode 4 may be measured. In this case, in step 106, the voltage of the backup power source 3 at the point A in FIG. 1 may be compared with the voltage obtained by subtracting the voltage drop of the diode 7 from the total voltage of each cell. By doing so, the A / D converter can be reduced by one in the microcomputer 13, so that the cost of the backup power supply system 20 can be reduced.

  In this embodiment, the example in which the voltages of the cells are summed in step 106 has been described. However, if the cell voltage detection circuit 12 directly measures the voltage of the backup power supply 3, it is not necessary to sum the voltages. Furthermore, in the present embodiment, an example in which one thermistor 14 is used to measure the temperature of the backup power supply 3 is shown, but a plurality of thermistors 14 may be used. Furthermore, in the present embodiment, steps 312 and 314 are exemplified to prevent overdischarge, but these steps may be excluded. And in this embodiment, although the backup power supply system for electronically controlled brake systems was illustrated, it does not wait that this invention is not limited to this.

  The present invention provides a backup power supply system that can determine the deterioration state of a lithium secondary battery constituting a backup power supply without using a resistor or a power supply for supplying a large current. Since it contributes to manufacturing and sales, it has industrial applicability.

1 is a block circuit diagram of a backup power supply system according to an embodiment to which the present invention is applicable. It is a flowchart of the backup routine which CPU of the microcomputer of a backup power supply system performs. It is a flowchart which shows the detail of the charging / discharging process subroutine of a backup routine. It is a flowchart which shows the detail of the backup power supply process subroutine of a backup routine.

Explanation of symbols

1 Main power supply 3 Backup power supply 4 Diode (first diode)
5 Load 6 Switch 7 Diode (second diode)
8 Load voltage detection circuit (load voltage detection means)
9 Reference voltage source 10 Changeover switch circuit (second changeover means)
11 Current detection circuit (current detection means)
12 cell voltage detection circuit (voltage detection means)
13 Microcomputer (control means)
14 Thermistor (temperature detection means)
15 Backup switching circuit (first switching means)
20 Backup power supply system

Claims (3)

A backup power source having a plurality of lithium secondary batteries and charged to a constant charge state by a main power source that supplies power to a load via a first diode;
Load voltage detecting means for detecting a load voltage applied to the load from the main power supply via the first diode;
A first switching means having a switch and a second diode, for supplying power from the backup power source to the load;
Current detection means for detecting a current flowing in the backup power supply;
Voltage detection means for detecting the voltage of the lithium secondary battery constituting the backup power supply;
Temperature detecting means for detecting the temperature of the backup power supply;
When it is determined that the load voltage detected by the load voltage detection means is lower than a preset voltage, backup power from the backup power supply is transferred to the load via the second diode of the first switching means. Control means for controlling the switch of the first switching means to be in an ON state so as to be supplied for a certain period of time
With
When the control means determines that the voltage of the main power supply is lower than the voltage of the backup power supply, even when the load voltage is higher than the set voltage, the switch of the first switching means is turned on and the backup power supply is turned on. Supplying backup power from a power source to the load through the second diode for a certain period of time, a current detected by the current detection means during the backup power supply, and a voltage detected by the cell voltage detection means The internal resistance of the lithium secondary battery is calculated from the temperature, and the temperature is corrected by the temperature detected by the temperature detecting means, and the lithium secondary battery is determined from the correspondence between the predetermined internal resistance after the temperature correction and the deterioration state. A backup power supply system characterized by determining a deterioration state of a battery.   2. The backup power supply system according to claim 1, wherein the control unit determines a deterioration state of the lithium ion battery every predetermined time for supplying backup power from the backup power supply to the load.   A reference voltage source that generates a reference voltage lower than the voltage supplied from the backup power source to the load, and a second switch that switches the load voltage detected by the load voltage detection means to the reference voltage generated by the reference voltage source And when the control means supplies the backup power from the backup power source to the load by turning on the switch of the first switching means, the load voltage detection means is connected to the reference voltage source. 3. The second switching means is switched so as to detect a reference voltage, and it is determined whether the load voltage detecting means and the first switching means are operating normally. The backup power system described in 1.

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